Why is anyone loyal to anyone? Just because you or I wouldn't be loyal to her, doesn't mean that others won't. I mean, look at Jaime, he's got all the reason in the world to not return to her, but he still does.
– MöozMay 13 '19 at 22:37

2 Answers
2

Qyburn was kicked out of The Citadel, stripped of everything, and treated like a degenerate and an outcast. He had been abandoned by everyone and he is awaiting execution when we first meet him in Season 3

Since arriving in King's Landing, Cersei has rewarded him, given him the freedom to pursue his many interests, honored him by making him her Hand, and most importantly she has always treated him with respect. She seems to be the only person to have ever done so, certainly the only person who was in a position of authority.

It could be argued that his loyalty to Cersei mirrors the loyalty that the Unsullied have for Dany. In Qyburn's mind, he probably saw himself as downtrodden and (metaphorically) shackled by small-minded people until Cersei set him free to fully express his genius.

It is customary in Westeros to uphold your vows. Tradition and honour are still highly-valued practices.

Qyburn is in the official position of "Hand of the Queen", he is in that role forever. He can't just decide to become disloyal, that's treason.

Besides, he has a lot to gain from being, and keeping that position. Cersei is messed-up enough to allow him to practice his, strange experiments. Previously, he had been dismissed from the Maesters in disgrace. So finding someone who at least in part shares his desire is important to him.

@curiousdanni Hand of the King is not a position associated with vows, and if you look at history as depicted ie in Fire & Blood, there is a very strong precedent for hands resigning dating all the way back to the first few Targaryen kings (because they were old, their children needed them, disagreements, &c.) Maesters, on the other hand, are meant to have no opinion over their lords, and do swear strong vows to serve for life.
– gntsknMay 14 '19 at 3:00

@gntskn Sure, but Mooz's answer says that Qyburn is the Hand of the Queen forever.
– curiousdanniiMay 14 '19 at 3:14

1

Forever, or until he resigns, is disbanded. I meant that it's a serious decision to make, Ned nearly lost his head at Robert's hands even before... losing his head.
– MöozMay 14 '19 at 3:19

Is it tho? Ned Stark was mocked by most of main characters for his honour(The Honorable Ned Stark). And each season has at least one treason or pathbreaking was shown.
– user28434May 14 '19 at 9:33